New HVAC for under $4k? Should I be worried?

[Jill Rossi]

I've gotten 3 quotes for a new 3.5 ton HVAC system to replace my old one.  One quote was $7400, one was $6500, and one was $3800.  Clearly $3800 sounds like the best deal, but is this too low to be legit? 

Thanks!

[David Dachtera]

@Jill Rossi,

Make sure the low bid is for a new, current technology system, not a "new old stock" system that they need to unload because it uses refrigerants which are being retired, such as R-22.